html{
    font-size: 10px;
}
@media only screen and (min-width: 320px){
    html {
        font-size: 56.25%!important; /* 9÷16=56% */
    }
}
@media only screen and (min-width: 375px){
    html {
        font-size: 62.5%!important; /* 10÷16=62.5% */
    }
}
@media only screen and (min-width: 414px){
    html {
        font-size: 68.75%!important; /* 11÷16=68.75% */
    }
}
@media only screen and (min-width: 500px){
    html {
        font-size: 75%!important; /* 12÷16=75% */
    }
}